Delve into the strange world of the twilight zone of the ocean

Editor’s note: This story was identified by the guest editor of “Call to Earth”, Kerstin Forsberg. She is a marine scientist and Rolex Award winner who helped ensure the national protection of giant mantas in Peru.

(CNN) – Dive into the ocean in the right place and you will end up entering the twilight zone. It is hundreds of meters deep, but not as far as the bottom of the ocean. And at that midpoint between light and shadow, science is making incredible discoveries.

The twilight zone of the ocean, formally known as the mesopelagic zone, lies about 200-1,000 meters below the surface. It is home to a wide variety of species, from the snuff until the vampire squid and the siphonophore It looks like a fairy light, and it’s a place where weirdness reigns. In the dark the eyes are small and the teeth large; many species are transparent, many bioluminescent. And in the dark, the dominant creature, the omnipresent bristling mouth, a fish of the family Gonostomatidae, it is smaller than the little finger of a human being.

It is an area that is difficult to study and often ignored by science, but new technology helps its exploration, forcing researchers to re-evaluate how much life is down there. Researchers now believe that the biomass is 10 or perhaps 100 times greater than previously believed, says Heidi Sosik, a senior scientist at the Woods Hole Oceanographic Institution (WHOI).

With each answer, more questions arise. “What we know now is how much we do not know,” he says.

Now this quest for knowledge has turned into a race against time.

Some scientists fear that commercial fishing operations could expand in this ecosystem, with small but abundant species ending up in fish oil, used in cosmetics and dietary supplements, or fishmeal, used in aquaculture to feed fish. species raised for human consumption.

“There are very basic things about the twilight zone that we do not know,” explains Sosik, such as the lifespan of some species and the time it takes to mature and reproduce. Without knowing the life cycles, there is no way of knowing how species can be fished sustainably.

Under pressure

Technology has long been a necessary friend to those who study the twilight zone. But it has not always been sufficiently advanced or nuanced to provide an accurate description of the region. For example, the bristly mouth fish. The Sonar equipment confused dense formations of these tiny fish with the seabed. Now researchers have the tools to estimate that up to a quadrillion (1,000 trillion) of them could live in the ocean, making it the most abundant vertebrate on Earth.

“The unique challenge of working in the twilight zone is that we don’t want to disturb the animals,” says WHOI lead scientist Dana Yoerger. These creatures are sensitive to light and sound, so monitoring them implies that the devices must be quiet and not agitate the water, and employ red lights that most animals cannot see.

Yoerger developed the ‘Mesobot’, an autonomous robot that discreetly watches over slowly moving wildlife. Using stereoscopic cameras to judge a creature’s relative position (in the same way that the human brain does), the robot moves with the animal at a fixed distance, allowing researchers to observe how it swims, hunts its prey, and documents delicate body structures that would be destroyed if a physical sample were caught in a net, he explains.

Trials have lasted up to 40 minutes, but Yoerger hopes to be able to track a target for 24 hours. “Ultimately, we would like Mesobot to think like a human scientific explorer, looking for the most unusual animals and observing their behavior for long periods,” he says.

In July, WHOI researchers will undertake the first phase of a study to map the twilight zone of the continental shelf of the northeastern United States. A team will deploy a network of sensors capable of tracking drifting research robots known as’minions«As well as marked specimens from upper waters entering the twilight zone, over approximately 1 million square kilometers.

Sosik explains that scientists are not only trying to understand the twilight zone, but also how it integrates into the ocean in general. “Whales and sharks, everything we are familiar with, the charismatic organisms of the ocean, the more we learn about them, the more they seem to depend on interaction with the twilight zone,” he says.

That sinking feeling

Researchers have also concluded that another species could also depend on the twilight zone: humans.

This ecosystem is known to play an important role in sequestering carbon in the ocean. In a process, which is part of what is known as the biological carbon pump, phytoplankton (microalgae that absorb carbon) that grow near the surface are consumed by zooplankton and fish that rise from the twilight zone at night. in what is believed to be the largest animal migration in the world. These creatures defecate, contributing to “sea snow,” a mix of matter that also includes dying organisms and bacteria.

Marine snow is consumed by marine life, including salps, gelatinous organisms that live both on the ocean surface and in the twilight zone and whose role may have been historically underestimated, Sosik says. Salps are capable of cleaning “enormous volumes of water,” he explains, and in turn excrete dense fecal granules that sink rapidly into the depths of the ocean.

Combined, the biological processes of the twilight zone absorb between 2,000 and 6,000 million metric tons of carbon per year, according to the WHOI: the lowest estimate equals twice the annual emissions of all the world’s cars.

The opportunity

The WHOI speculates that commercial fishing could upset the balance of the twilight zone carbon pump, with knock-on effects for the weather. The organization claims that the economic value of more accurate data could be worth hundreds of billions of dollars and it could help society make better decisions, a compelling argument for further investigation.

“In the past, humans found living resources in the ocean and went headlong to overexploit them,” says Sosik, “and in hindsight we realized that we should have been more informed and taken a more conscious approach. With the twilight zone we have that opportunity.

As most of the twilight zone is outside national jurisdictions, an international effort is underway to ensure good administration. The UN endorsed a consortium known as JETZON (Twilight Zone Ocean Joint Exploration Network) to coordinate research, share technology and results, and inform policy makers.

The consortium led by National Oceanography Center of the United Kingdom, brings together projects from the WHOI and entities from five other countries, as well as the European Union, in order to answer questions such as the amount of marine snow that falls through the twilight zone and how biodiversity influences the biological carbon pump.

“We have this incredible opportunity to bring together basic science and curiosity-driven science, and try to generate solutions for the great challenges that humans face when interacting with our planet and our ocean ecosystems,” says Sosik.